The essential objective of the Materials Science Core is to provide well defined and specifically designed nanoparticles (NPs) that allow the objectives of the three research projects to be addressed. Although materials preparation for any biological or toxicological study is not necessarily a simple task, the challenges of assuring that the physicochemical properties and structural arrangement of engineered NPs used for biological studies are well established at the time of actual use are significant. It is increasingly recognized that individual NPs can be altered by the method of analysis, can change structure or chemical state in different environments, and may change as a function of time. In addition, properties of particles and collections of particles are influenced by aggregation, the presence of impurities and the nature of deliberate or adventitious coatings. Therefore, in addition to preparing NPs of the desired size, composition and structure, and surface chemistry, it is essential to confirm the nature of the particles at the time of use and to have an understanding of how the particle properties and particle distributions vary with time in the environments of interest. Three different oxide NPs, cerium oxide (ceria), iron oxide, and silica have been identified as the 'primary' particles to be examined in the biological studies. Members ofthe Materials Science research team have experience with the synthesis and characterization of NPforms of these three materials. Our experience with the synthesis and characterization of particles of the desired size (and size distribution), composition and surface chemistry (or surface functionalization) will be used to achieve the goals of the Core. The team has the background and experience to design and prepare oxide NPs that will enable the PNNL U19 Program to accomplish their three research objectives; Aim 1. Synthesize and characterize the 'primary' nanoparticles desired for biological studies with well defined physicochemical properties. Aim 2. Design and synthesis of nanoparticles optimized for counting and tracking in biological environments. Aim 3. Understand the impact of different environmental conditions on the time-dependent properties ofthe primary and coated nanoparticles.